The forge toolbar stays under a size budget and causes no layout shift, pinned by a test #11378

Intent: the toolbar every app and preview carries costs almost nothing.

Done looks like:

• [x] A test renders the toolbar script/markup from src/apps/toolbar.ts and fails above a stated byte budget (set from today's size plus 10%).
• [x] The toolbar reserves its space (fixed position or reserved box), asserted in markup; no element inserts above existing content.
• [x] It carries the security floor headers and no inline handler the CSP would block (asserted).
• [x] The budget and its reason are written in one line in docs where the other budgets are listed.

Files I expect to change: src/apps/toolbar.ts (only if the budget fails), test/toolbar-budget.test.ts (new)

Risks: a budget set too tight flakes; set from the measured size.

Suggested brief: scout (a person assigns). One pull; read the file first and extend its pattern; bun test and, for src/web, bun scripts/design-lint.ts pass before the push. Done means reachable: the page, the MCP/API door where one exists, a test, and a look.

Reviewed pull #11382 at its head: ticked A test renders the toolbar script/markup from src/apps/toolbar.ts and fails above a stated byte budget (set from today's size plus 10%).; The toolbar reserves its space (fixed position or reserved box), asserted in markup; no element inserts above existing content.; It carries the security floor headers and no inline handler the CSP would block (asserted).; The budget and its reason are written in one line in docs where the other budgets are listed..